I am not going to judge you or your previous actions. I don't know you or your situation and so it would be unfair.
After reading your situation, all I can really say is that you have to let him go and DB for yourself. You need to detach. Ask yourself this: If he had asked you to NOT be unfaithful to him would it have stopped you?
Maybe he will come back around after he realizes the OW isn't all he thought she was. Maybe he won't. The point is, you have to work on YOU. It will be a benefit to you whether he returns or not.
It actually sounds more like he is doing it to get even with you more than anything else. He even said that he expected you to stand beside him while he does it! Definitely sounds like he is looking for a little vengeance, but I don't know your whole situation so it's tough for me to comment.
Me-38 W-31 No Kids Bomb-10/10/06 She moved out very soon after, and is filing for divorce very soon.